Main article: List of Sanctuary episodes
Sanctuary follows the exploits of Dr. Helen Magnus (Amanda Tapping) and her quest to protect what most people would consider monsters. "The Sanctuary" serves as a safe haven for these "Abnormals". She is aided in her quest by her reluctant protégé Will Zimmerman (Robin Dunne); her intrepid, if somewhat reckless, daughter Ashley (Emilie Ullerup); the talkative geek Henry Foss (Ryan Robbins), a computer and security expert; and her taciturn Neanderthal-like unnamed assistant, sometimes called "Big Guy" (Christopher Heyerdahl).

The first season reveals the history of Dr. Helen Magnus, stating that in her youth she was a member of a group of experimental scientists known as "The Five", which included also Nikola Tesla, Nigel Griffin, Dr. James Watson, and John Druitt; who wanted to push the boundaries of their understanding of the physical world through unconventional means. At some point during their partnership, Magnus acquired a vial of untainted vampire blood and used it in a serum that "The Five" injected into themselves. After the injection, they each developed different gifts; Magnus gained a high level of longevity, Nigel Griffin acquired the power of invisibility, Dr. James Watson's intellect was tremendously heightened, John Druitt developed the ability to teleport through time and space, and Nikola Tesla undergoes transformation into a vampire, with the additional power of limited electrical manipulation.

In the second half of the first season, "The Cabal", a powerful shadow organization that captures, studies, and experiments on Abnormals in the belief that the Abnormal population is a threat to the human species, is introduced. During the season one finale, "Revelations", they test a small amount of a biological weapon named Lazarus, that causes all types of Abnormals to become extremely violent, attacking anyone nearby, before they painfully die. This is part of The Cabal's overall plan to incite humanity against the Abnormals so that they can wipe out the entire Abnormal population and gain a greater amount of power over humanity.